The purpose of this project is to test the hypothesis that adenosine deaminase (ADA), a key enzyme in purine metabolism plays an essential role in early postimplantation development. ADA catalyzes the irreversible deamination of adenosine and 2'- deoxyadenosine. This is an important reaction because both ADA substrates are potent inhibitors of cell growth, especially in the developing fetus and embryo. This proposal derives from preliminary results showing that a pronounced increase in ADA activity occurs at the maternal/embryonal interface in pregnancy, starting on day E6.5 of gestation in the mouse, and treatment with the ADA inhibitor 2'-deoxycoformycin (2'dCF) is embryolethal during this induction. The experiments propose to address the (I) molecular expression and (II) biologic function of ADA during early postimplantation development in the mouse. Pertaining to the former, the objective is to localize the active sites of ADA synthesis. ADA-specific complementary DNA (cDNA) sequences will be used to probe the embryo, extraembryonic membranes and maternal decidua for ADA mRNA in Northern blots and to spatially localize these transcripts by in situ hybridization. Based on preliminary results, it is expected that maternal decidual cells exhibit the highest capacity for ADA synthesis. Pertaining to biologic function, the objective is to investigate the cause of embryolethality induced by 2'-dCF. It will first be determined if 2'dCF promotes the accumulation of ADA substrates. Adenosine levels will be measured in the embryo in HPLC, and substances known to antagonize action, such as caffeine, will then be used to try and ameliorate embryolethality. Next, it will be determined whether 2'dCF acts on the embryo directly or through a maternal effect. Alterations in the normal tissue-specific patterns of proto-oncogene expression, monitored by mRNA abundance in quantitative dot-blots, will be analyzed as indicators of abnormal development in vivo and in embryo culture. Using this approach, the tissue-specific consequences arising from direct exposure to 2'-dCF in the absence of maternal decidua can be compared to those arising from in utero exposure. The expression of ADA at the maternal/embryonal interface is a target that can be studied by modern, sensitive molecular methods in attempting to define the cause of abnormal embryonic development.